For a year, the 2016 presidential campaign has sparked the use of the word "unprecedented" in a way that has been, well, unprecedented.

Put this on that list.

In the two weeks before Election Day, FBI Director James Comey dispatched a pair of bombshell letters that first announced a revived investigation of Hillary Clinton's emails and then concluded, basically: never mind.

That hasn't happened before. The closest parallel might be the announcement four days before the 1992 election that former Defense secretary Caspar Weinberger was being indicted in the Iran-contra affair, a step that enraged the embattled George H.W. Bush. (Bush would lose his re-election bid but pardon Weinberger before he left office.) This time, analysts in both parties believe the initial Comey letter has had consequences that can't be reversed by the follow-up letter nine days later — an interval when 40 million Americans cast early ballots.

For one thing, it staunched rising momentum for Clinton, causing enough concern that she largely shelved plans to adopt a more positive message in the campaign's close in favor of continued attack on her rival.

For another, it got Trump out of the spotlight for vulgar comments on the Access Hollywood video and back on offense. He and his allies used word of a new FBI investigation and an erroneous report on Fox News to argue that Clinton was about to be indicted.

Down the ballot, the renewed controversy prompted Democratic strategists to lower their calculations on the number of House and Senate seats their candidates were likely to pick up.

And it plunged the FBI, the nation's most powerful law enforcement agency, into the sort of partisan furor that this year also has eroded public faith in the news media, the two major political parties and the election process itself.

Imagine, for instance, the first meeting between the FBI director and the president-elect, whichever candidate wins. Clinton's allies have blasted his judgment in sending the first letter; Trump has accused him of bending to political pressure in sending the second.